MAGNETISM AND COVALENCY IN THE 2-DIMENSIONAL 3-BAND PEIERLS-HUBBARD MODEL

Stoichiometric phases and doping states are studied in a two-dimensional, three-band extended Peierls-Hubbard model, using an inhomogeneous Hartree-Fock approximation. Magnetism and covalency are investigated in a parameter space of strong intersite electron-lattice coupling and varying on-site electron-electron repulsion strength. In a crossover region between a charge-density-wave phase driven by intersite electron-lattice coupling and an antiferromagnetic phase driven by on-site electron-electron repulsion, a bond-order-wave state, a spin-Peierls state, and a mixed state of spin-Peierls bonds and antiferromagnetic spins axe found to be stable and caused by competing magnetism and covalency of different relative strengths. Doping states depend qualitatively upon the nature of these global phases. In particular, separation of spin and charge is observed in the background of the bond-order-wave state as a consequence of local competition between magnetism and covalency.